A steel sheet for aluminum plating HPF (Hot Press Forming) is commonly manufactured by immersing a steel sheet having high hardenability in a plating bath with Al as a base, and a plated steel sheet having an Al plating layer on the surface is subsequently heat treated to be widely used in manufacturing articles for automobiles having a complex shape and strength of 1300 MPa or greater.
However, during a HPF heat treatment process, the plating layer may have a structure having an alloyed layer including an intermetallic compound such as FeAl, Fe2Al5 or the like as an upper layer, and a diffusion layer formed with 80% by weight to 95% by weight of Fe (hereinafter, compositions of steel components are all provided in % by weight) as a lower layer. However, the alloyed layer on the upper side in the plating layer may be brittle as compared to the diffusion layer, and is removed from the plating layer during press forming and adsorbed on a pressing surface, which may be disadvantageous, making continuous press forming difficult.
In detail, in a hot press formed (HPF) article prepared by forming a hot dip aluminum plating layer on a substrate steel sheet and high temperature forming thereafter, the plating layer is formed to have a soft diffusion layer and a hard alloy layer, and a breakage may occur at an interface of the diffusion layer and the alloy layer during high temperature hot processing. Then the broken plating layer may accumulate on a mold in fine powder form, and in some cases, may adhere to the mold and cause various issues such as size changes in the hot press formed (HPF) article, surface dent occurrence, mold modification and cutting work, and additional costs may be incurred.
When such problems occur, companies receiving and hot processing the material bear extra costs, and automobile companies may also face significant losses since production delays may inevitably occur. Consequently, there has been demand for the development of hot press formed (HPF) articles having excellent press formability in which problems described above have been overcome.